1. Field of the Invention
The present invention relates to an odor filter and/or pollutant filter for air supply ducts, for example, in air conditioners, motor vehicles and means of transportation. The invention more particularly relates to such a filter having an adsorption filter bed.
2. Description of the Prior Art
Conventional particle filters based on current knowledge are not sufficient to purify air flows (e.g., in air conditioners, supply air for motor vehicles, etc.) because they are unable to retain gaseous components, in particular, odors or pollutants. The impact of such inabilities on health and well-being were largely underestimated in the past. To overcome this problem an adsorption filter was added after the particle filters.
Today, adsorption filters are manufactured primarily on the basis of activated charcoal. In stationary units, thin packings are used, but these are not suitable for use in motor vehicles. Packed filters always entail a compromise with respect to particle size: the absorption kinetics require small adsorbent particles, but for the sake of a smaller pressure drop the particles should be large. Furthermore, gas formation can easily occur. Also, maintaining or exchanging the filter becomes more difficult and greater contamination occurs. The development of the "expanded fixed bed" principle largely eliminated these disadvantages.
According to this principle, small adsorbent particles are affixed to an open substrate structure, which usually is shaped like a flat sheet. In this way, the compromise on particle size is avoided. Furthermore, the flat low-dust filter elements are easy to exchange, making maintenance significantly less labor-intensive than it is in the case of conventional filters. For air supply ducts in motor vehicle cabins, flat filters as well as folded filters have been introduced or are under development. Flat filters may be constructed of activated charcoal particles which adhere to one another as well as according to the "expanded fixed bed" principle. These filter media are fixed or foamed into a frame by means of a seal, and this frame is installed in the air supply duct. A significant disadvantage of these filters is that they have an increased space requirement due to their frames and seals. Furthermore, these filters are complicated and thus expensive to manufacture. Significant problems also arise during their disposal or recycling, because the various materials permanently connected to one another interfere with the requirement to separate materials.